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Ever passed by a mirror in a curious place and wondered if it may have been a two-way mirror?

Take time with this 5 minute read to protect yourself with these two-way mirror finding tips.

By using the fingernail test you can detect a glass two way mirror!

A two way mirror is a transparent mirror that can look exactly like a regular mirror when the back side of it is dark. Don’t worry, there is more than one way to tell the difference!

Contents

Test #1

Fingernail Test

Test #2

Tint Comparison

Test #3

Hollow Sound

We have a series of three tests to use to confirm that the mirror you see in front of you is not a two way mirror.

Test #1: The Fingernail Test

What is the fingernail test?

Place your fingernail to the front of the mirror. You can test to see which side the reflective coating is facing. For glass two way mirrors, the mirror coating has to be facing you.
 
If your fingernail’s reflection touches itself, that is the coated side. If there is a gap between your finger and its reflection, go to Test #2.

The Fingernail Test Rules Out the Glass Two Way Mirror

The glass two way mirror is one-directional. You can only install it with the mirror coating facing forward so it is easy to spot using this test.
 
The acrylic two way mirror and glass smart mirror are not one-directional. You must use the next two tests to be sure it is not a two way mirror in this case.
fingernail-test-with-acrylic-and-glass-two-way-mirrors

More on the Glass Two Way Mirror

The glass two way mirror has a mirror coating that is 70% reflective. It only allows 11% of the light through the mirror. It is on a dark grey substrate, which makes it one-directional. The glass two-way mirror cannot cheat the fingernail test. The reflection coating must be facing the room that is being observed. That way the people being observed are only seeing their reflection. On the opposite side, the darker room is located where the observer will be watching.

Notice the fingertip’s reflection touching itself. Very different from that of the standard mirror’s reflection.

The light is even on both sides of the mirror in this picture. You are able to see through the semi-transparent glass at the moment.

Front

Side

Back

Glass two-way mirror cannot cheat the fingernail test. The reflection coating must be facing the room that is being observed. That way the people being observed are only seeing their reflection. On the opposite side, the darker room is located where the observer will be watching.

Test #2: Tint Comparison

How does a two way compare to a standard mirror?

All three mirror types we are looking at in this article have a 70% reflection. A standard mirror is 94% reflective. This means that it will have a darker tint than a standard mirror.

Bring a Small Makeup Mirror With You

To do this test, simply pull out a standard mirror from your purse or pocket. Put it up next to the mirror and check to see if the tint looks the same as your mirror. If it appears darker, it is likely a two way mirror.

More on the Acrylic Two Way Mirror

70% reflective with 25% light transmission on a grey substrate, acrylic two way mirror is reflective from both sides of the substrate. Meaning it can be installed either way. If installed backwards ( the coated side on the back ) it can cheat the fingernail test looking like the reflection of a standard mirror! Something to think about if you are testing a questionable mirror. Acrylic tends to have a different feel than glass. Rubbing your nail gently across the surface may help you determine if you have found an acrylic two way mirror, or a standard glass mirror.

Acrylic two way mirror will closer match the reflection tint of a standard mirror as well. Whereas glass two way mirror tends to have a bronze tint.

More on the Glass Smart Mirror

Smart mirror is similar to the acrylic two way mirror in properties. It has a 70% reflection with a 25% light transmission. Its reflective from both sides of the substrate. Smart mirror can be installed backwards as well ( the coated side on the back ) it can cheat the fingernail test looking like the reflection of a standard mirror!

If you are testing a questionable mirror, smart mirror tends to have a warmer tone on the reflective coating. Observe the smart mirror on the right compared to the standard mirror reflection of the mug on the left.

Test #3: Knock on the Mirror

Listen for a Hollow Sound

If you are worried about a two way mirror and the first two tests did not work for you, try knocking on the mirror gently. If there is a hollow sound going on instead of a more solid sound, it is possible that the area behind the mirror is open instead of the mirror being just mounted to the wall. This could reveal that there is an observation area or a camera behind the mirror. Be careful out there!

Did you know?

Two-way mirrors are dependent upon the lighting in the room. Both sides of the mirror cannot be evenly lit for the illusion to work. The observer side of the mirror must be at least half as dark for the reflection coating on the other side to properly reflect light back at those being observed.

Want to see samples of two way mirrors?

Visit our ORDER SAMPLES page.

CONCLUSION: Now that you are armed with knowledge, never be afraid of a sketchy looking mirrors again. Just remember the fingernail test & a makeup mirror.

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